1. Field of the Invention
The invention is related to the field of communication networks and, in particular, to providing call delivery to a dual mode wireless device.
2. Statement of the Problem
Wireless phone providers are developing dual mode phones that have the functionality for communicating with a cellular network (e.g., CDMA or GSM) and another type of wireless data network, such as a WiFi network (e.g., 802.11b, 802.11g, etc). The concept of the dual mode phone is to allow a user the flexibility to communicate with either the cellular network or a WiFi network. WiFi networks are typically used for data communications such as Internet browsing, email, etc. WiFi networks may also be used for voice communications in the form of VoIP calls. Cellular networks are typically used for voice communications, but have also been adapted for data communications.
The dual mode phones take advantage of local WiFi “hot spots” in a corporation or enterprise, airports, book stores, coffee shops, etc, that are becoming more common. When a dual mode phone is in range of a WiFi hot spot, the phone may access the Wireless LAN (WLAN) for data communications, VoIP calls, etc. The WLAN generally provides a higher bandwidth than cellular networks for more efficient data transfer. If the dual mode phone roams out of a WLAN, then the phone can switch over to the cellular network for voice or data communication.
A WiFi network may be integrated with an IP Multimedia Subsystem (IMS). The 3rd Generation Partnership Project (3GPP) has set forth specifications describing the architecture of IMS networks and networking. Service providers are accepting this architecture in next generation network evolution. The IMS architecture is initially defined by the 3GPP to provide multimedia services to mobile subscribers over an IP network. IP networks have become the most cost savings bearer network to transmit video, voice, and data. IMS uses the advantage of IP networks to provide multimedia services for IMS subscribers on an IMS platform. The signaling used within IMS networks is generally Session Initiation Protocol (SIP). IMS defines the standard SIP interface between application servers (AS), the IMS core network (CSCF), the IMS subscriber (user), the IMS database (HSS), and IMS billing elements.
The capability of a phone communicating with two different types of wireless networks creates networking issues. For instance, if a calling party dials a number for a mobile subscriber having a dual mode phone, that call may be routed to the phone over either the cellular network or the WiFi/IMS network. One problem facing network managers is call delivery when there are two wireless networks available to the dual mode phone. More particularly, network managers need to determine which network to route the call over so that it may be received by the dual mode phone. There are currently no standards available to address the call delivery issues for dual mode subscribers.
Another problem created by mobile subscribers is that they may roam in and out of service areas of the wireless networks (cellular and WiFi/IMS). When a dual mode phone is in range of a cellular network, the dual mode phone registers with the cellular network. Similarly, when the dual mode phone is in range of the WiFi/IMS network, the dual mode phone also registers with the WiFi/IMS network. A subscriber database in the cellular network (e.g., Home Location Register (HLR)) and a subscriber database in the WiFi/IMS network (e.g., Home Subscriber Server (HSS)) each store a subscriber record that indicates if the dual mode phone is presently registered.
After the dual mode phone is registered in the wireless networks, the mobile subscriber may roam out of the service area of one or both of the networks. This may particularly be a problem in WiFi/IMS networks as the service areas are generally small as compared to the service areas of well established cellular networks. As an example, if the mobile subscriber is in a downtown of a city, the mobile subscriber may be in range of a WiFi/IMS network provided by coffee shops, restaurants, etc. If the mobile subscriber walks two or three blocks away from the downtown area, the WiFi/IMS network may be out of range. Even if the mobile subscriber moves out of range of the WiFi/IMS network, the subscriber database of the WiFi/IMS network may still indicate that the dual mode phone of the mobile subscriber is registered with the network. If a call is received for the mobile subscriber, the WiFi/IMS network will attempt to connect the call to the mobile subscriber because the dual mode phone is still indicated as registered. The WiFi/IMS network may spend unnecessary time trying to connect a call to the dual mode phone that is no longer in range of the WiFi/IMS network. For instance, in an IMS network the Call Serving Control Function (CSCF) receiving the call to the dual mode phone will transmit a SIP INVITE message to the dual mode phone and wait for a response (e.g., a SIP 200 OK message). If no response is received after a time period, then the CSCF will transmit a SIP TRYING message to the originating network of the call (e.g., the PSTN). The CSCF may also transmit another INVITE message to the dual mode phone and wait again for a response. Depending on how the IMS network is provisioned, the CSCF may transmit several messages to the dual mode phone and several messages to the originating network in an attempt to connect the call to the dual mode phone. If the CSCF is unsuccessful in connecting the call, which will be the case if the mobile subscriber is out of range of the WiFi/IMS network, the CSCF will then initiate secondary call treatments for the call, such as routing the call to voice mail.
If the mobile subscriber does not move back into a service area of the WiFi/IMS network, the WiFi/IMS network will eventually end the registration of the dual mode phone (also referred to as a time out). Unfortunately, the time out of a dual mode phone may be an hour, two hours, or more during which time the WiFi/IMS network may be wasting time trying to connect calls to the dual mode phone.